Spectral cones in Euclidean Jordan algebras Juyoung Jeong Department of Mathematics and Statistics University of Maryland, Baltimore County Baltimore, Maryland 21250, USA
[email protected] and M. Seetharama Gowda Department of Mathematics and Statistics University of Maryland, Baltimore County Baltimore, Maryland 21250, USA
[email protected] August 2, 2016 Abstract A spectral cone in a Euclidean Jordan algebra V of rank n is of the form K = λ−1(Q); where Q is a permutation invariant convex cone in Rn and λ : V!Rn is the eigenvalue map (which takes x to λ(x), the vector of eigenvalues of x with entries written in the decreasing order). In this paper, we describe some properties of spectral cones. We show, for example, that spectral cones are invariant under automorphisms of V, that the dual of a spectral cone is a spectral cone when V is simple or carries the canonical inner product, and characterize the pointedness/solidness of a spectral cone. We also show that for any spectral cone K in V, dim(K) 2 f0; 1; m − 1; mg, where dim(K) denotes the dimension of K and m is the dimension of V. Key Words: Euclidean Jordan algebra, spectral cone, automorphism, dual cone, dimension AMS Subject Classification: 15A18, 15A51, 15A57, 17C20, 17C30, 52A20 1 1 Introduction Let V be a Euclidean Jordan algebra of rank n and λ : V!Rn denote the eigenvalue map (which takes x to λ(x), the vector of eigenvalues of x with entries written in the decreasing order). A set E in V is said to be a spectral set [1] if there exists a permutation invariant set Q in Rn such that E = λ−1(Q): A function F : V!R is said to be a spectral function [1] if there is a permutation invariant function f : Rn !R such that F = f ◦ λ.